4.3.4 Advanced mapping techniques

As mentioned earlier, very large maps cannot be observed in the conventional On-The-Fly mode. If you have sources which are larger than about 10' in both direction, you should consider using Fast OTF Mapping. Fortunately, the command syntax is the same as for normal maps, just the numbers are different:

   OBST> cmap /maps 1600 8 1080 54 /time 100 /skew 27
   OBST> start

will observe a skewed $27' \times 18'$ map (edges skewed by $45^{\circ}$) with 21 subscans and a total integration time of 35 minutes.

Another option of mapping is to scan not along Azimuth, but rather along Right Ascension, or - even this is possible - along a coordinate rotated by a certain angle relative to Right Ascension. This gives you full control over the orientation of your map on the sky and may be useful to optimally place your map for a certain source. The corresponding command includes the scanning direction as fifth parameter of the /mapsize option and could be for example:

   OBST> cmap /mapsize 1200 10 1200 50 LAM /time 80

This would perform a rectangular map of $20' \times 20'$ in R.A.-Dec. or - if you have defined your source in the catalog in descriptive coordinates, i.e. using SBAS 1D or SBAS -1D and SL0P, SB0P, and the angle SK0P intead of SLAM and SBET - in a source-specific coordinate system. See Section 6.8.9 for the various mapping options, and ask the FoT how to set up your catalog sources with a descriptive coordinate system.

Important: Since the data reduction software currently available uses the EKH algorithm for map restoration, it can only handle maps where the scanning direction is the same as the wobbling direction. In other words: You must scan in Azimuth if you want to use NIC or MOPSI for data reduction! If you want to use any other scanning direction, you have to provide your own data reduction software. In this case, please contact the SMTO staff well in advance to make sure that your software will run on our computers and to discuss data format issues.